Various structures have been proposed regarding drive devices for vehicles including, as a driving force source, a rotating electrical machine capable of functioning as a motor, such as, for example, electric vehicles and hybrid vehicles. The structure including independent rotating electrical machines for driving two driving wheels is already known in the art.
For example, a vehicle drive device described in Japanese Patent Application Publication No. JP-A-H05-116542 includes left and right output members respectively connected to left and right driving wheels, left and right rotating electrical machines respectively drivingly connected to the left and right output members, and left and right deceleration devices each formed by a planetary gear mechanism provided between the corresponding output member and the corresponding rotating electrical machine. The output members, the rotating electrical machines, and the deceleration devices are provided coaxially in this vehicle drive device. Since this vehicle drive device is structured to include independent rotating electrical machines for the right and left driving wheels, respectively, the rotating electrical machines is reduced in size and weight, and the transmission efficiency of the driving force is improved, as compared to the case where the left and right driving wheels are driven by a common rotating electrical machine. Moreover, since this vehicle drive device includes the left and right deceleration devices formed by the planetary gear mechanisms, output rotation of the rotating electrical machines is appropriately decelerated and transmitted to the respective output members, and a required driving force is ensured.
In the above vehicle drive device, however, the rotating electrical machines, the deceleration devices, and the output members are provided coaxially. Thus, the positions of the rotating electrical machines are restricted, and the overall size of the device tends to increase in the axial direction. Thus, there are significant restrictions on mounting on vehicles, and dimensional restrictions are also significant when the rotating electrical machines are increased in size in order to improve the driving force. Moreover, since the device has a large overall dimension in the axial direction, an axle connecting the output members and the driving wheels tends to have a short axial length. Thus, a deflection angle of the axle increases due to vertical movement of the driving wheels, thereby imposing a large load on bearings that support the output members connected to the axle. Thus, the bearings are increased in size in order to ensure durability thereof, causing a further increase in overall dimension of the device.
Moreover, since the positions of the rotating electrical machines are restricted to the positions coaxial with the output members, it has been difficult to lower the mounting positions of the rotating electrical machines to lower the center of gravity. Moreover, since the planetary gear mechanisms are used as the deceleration devices, the reduction gear ratio is substantially limited to about 3 to 4, and it has been difficult to obtain a reduction gear ratio larger than about 3 to 4. Thus, it has been difficult to increase the reduction gear ratio to increase the rotational speed of the rotational electrical machines, and thus, it has been difficult to reduce the size of the rotating electrical machines while ensuring a required driving force.